Infection rates in spine surgery at typically below 3% whereas the rates in instrumented spine surgery range from 1-17%. The increased rate of infection is thought to be attributable to the use of synthetic biomaterials, longer procedure times, and more severe disease conditions that merit the placement of orthopedic implants.
It is strongly suspected that the presence of a synthetic biomaterial in a wound will increase the infection rate by two means—foreign body response and biofilm formation. Foreign body response is the body's reaction to any implanted material and typically creates a local hyper-immune response to the presence of a foreign material. Biofilm formation occurs when bacteria colonize a biomaterial surface and create a mucous layer to protect the colony from the host immune system. Once a bacterial biofilm has formed, it is unlikely that the immune system can resolve the infection.
One way to prevent device colonization is to apply a coating that prevents biofilm formation or has native antimicrobial properties. Unfortunately, applying coatings to spinal and orthopedic instrumentation is not trivial and most coatings fail to preserve some aspects of the device's mechanical function. Specific to spinal instrumentation, a coating must not compromise the mechanical nature of the implanted instrumentation. It has been demonstrated that most coatings degrade the strength of the device's mechanical interconnections.
The following documents are pertinent to this discussion: US Patent Publication 2004/0142013(Rubsamen); U.S. Pat. No. 5,476,462 (Zimmer); U.S. Pat. No. 5,281,222 (Zimmer); U.S. Pat. No. 5,312,402 (Synthes); U.S. Pat. No. 5,423,818 (Danek); U.S. Pat. No. 6,770,075 (Howland); US Patent Publication 2007/0093814 (Callahan); US Patent Publication 2004/0143264 (McAfee); PCT Patent Publication WO 2006/118866 (SDGI Holdings); U.S. Pat. No. 5,486,174 (Soprane); U.S. Pat. No. 7,270,665 (SDGI Holdings); US Patent Publication 20070156143 (Zimmer Spine); PCT Patent Publication WO2007089984 (Warsaw Orthopedic); PCT Patent Publication WO2003023401; U.S. Pat. No. 7,226,612 (Chienna); U.S. Pat. No. 7,175,611 (Mitchnick); U.S. Pat. No. 6,575,945 (Prosl); U.S. Pat. No. 6,596,338 (Scott); U.S. Pat. No. 6,706,024 (Modak); U.S. Pat. No. 6,514,517 (Jamiolkowski); U.S. Pat. No. 6,746,773 (Llanos); U.S. Pat. No. 6,338,904 (Patnaik); U.S. Pat. No. 6,264,936 (Sawan); US2003/0229319 (Mitchnik); US Patent Publication 2004/0137065 (Vogt); US Patent Publication 2004/0099762 (Zhang); US Patent Publication 2003/0147960 (Lin); U.S. Pat. No. 5,281,419 (Tuan); U.S. Pat. No. 5,268,178 (Calhoun).